Heretofore, anti-galling compositions containing solid lubricants such as nickel and graphite have been well known in the art as useful on various metal surfaces at elevated temperatures. These compositions are generally oil based and tend to migrate once applied, creating imprecise application and inconvenient and messy handling. Because these compositions tend to migrate, they often come in contact with areas of a part which should be kept free of lubricating materials. The use of these compositions on numerous applications where cleanliness, precision and speed are required, is precluded due to their unmanageable nature.
Other prior art dry lubricants have been developed in conjunction with electrolytic plating techniques. For example, U.S. Pat. No. 3,756,925 to Takeuchi et al., describes a dry lubricant coating comprising a graphite flouride powder, which is just treated with a dispersion promoter, and then immersed in a metal plating bath. The graphite flouride dispersion is then deposited electrolytically onto a surface as a lubricative coating.
Various combinations of graphite and molybdenum disulphide have been known to be effective lubricative coatings. U.S. Pat. No. 4,243,434, to Hartley, describes such a combination dispersed in an aqueous phosphate metal binder. These coatings are useful in prolonging the useful life of cutting tools and other such objects subject to high abrasive contact.
Lubricative compositions containing molybdenum are not effective in applications involving threads (e.g. nuts and bolts assemblies) where lubricity is required to facilitate the turning of a nut on a bolt or a bolt into a flange. Molybdenum is a hard, dense material which tends to resist compression. This interferes with the torquing-on of a nut onto a bolt, thereby increasing the amount of torque required to seat the nut against the flange.
Similarly, disassembly of a nut, the threads of which are coated with molybdenum, demonstrates the same problem, particularly after a nut and bolt assembly has been loaded to a particular tension and exposed to extreme temperature conditions, e.g., between 800.degree.-1200.degree. F. Seizing and galling of the threads are frequent with such compositions.
It is evident that a need exists which overcomes the deficiencies of the prior art, yet maintains all its advantages. The instant invention is a dry-to-the-touch, non-migratory, high temperature, anti-galling and lubricating composition which can be applied to a surface, particularly a metal surface, via any suitable method, e.g., dipping, painting, rolling, spraying, etc., and which retains its lubricative properties at temperatures up to 1200.degree. F.
The composition comprises a dispersion or suspension of graphite powder or metal powder, or both, in an aqueous carrier containing a polymeric binder, said graphite powder being present in the amounts of about 5% to about 70%, and said metal powder being present in the amounts of about 0% to about 90%. Percents are based on the weight of the total composition.
This invention also relates to a process of coating a surface with a dry, non-migratory coating, as well as to a threaded object coated with the disclosed composition.